<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>浮动的问题</title>
    <style>
        .box{
            width: 100px;
            height: 100px;
            background-color: greenyellow;
        }

        .left{
            float: left;
        }
        .clear-fix{
            clear: both; /*left/right/both*/
        }

    </style>
</head>
<body>
<div class="box left">
    hello
</div>
<div class="clear-fix">
    world
</div>
</body>
</html>